1. Field of the Invention
The present invention relates to a keypad used in a portable terminal, and more particularly to a keypad with a light guide panel and a keypad assembly.
2. Description of the Related Art
Generally, a keypad used in a portable terminal includes a plate-shaped elastic pad, a plurality of key tops disposed on the upper surface of the elastic pad with numbers and characters printed on the upper surface thereof, respectively, and a plurality of protrusions (or actuators) projected downwardly from a lower surface of the elastic pad. In addition, the typical keypad has a plurality (generally 15 to 20) of light emitting devices for backlighting the keypad.
FIG. 1 is a cross-sectional view of a keypad assembly in the prior art. The keypad assembly 100 includes a keypad 110, a switch board 150 and a plurality of light emitting diodes (LEDs) 170.
The keypad 110 includes a plate-shaped elastic pad 120, a plurality of key tops 140 formed on an upper surface 122 of the elastic pad 120 with numbers and characters printed on the upper surface thereof, respectively, and a plurality of protrusions 130 projected downwardly from a lower surface 124 of the elastic pad 120. Each of the protrusions 130 is aligned with the center of the corresponding key tops 140. Also, the elastic pad 120 has a plurality of grooves 126 on the lower surface 124 thereof. The grooves 126 are positioned around the respective protrusions 130 to prevent the LEDs 170 from interfering with the protrusions 130.
The switch board 150 includes a plate-shaped PCB (printed circuit board) 155 and a plurality of switches 160 formed on the upper surface of the PCB 155 that faces the keypad 110. Each switch 160 consists of a conductive contact member 162 and a conductive dome 164 that completely covers the contact member 162.
The plurality of LEDs 170 are mounted on the upper surface of the PCB 155 and covered by the corresponding grooves 126 of the elastic pad 120.
When a user presses a specific key top 140, a portion of the keypad 110 below the pressed key top 140 is deformed towards the switch board 150. As a result, a corresponding protrusion 130 formed at the deformed portion of the keypad 110 presses a corresponding dome 164 which will then be in electrical contact with a corresponding contact member 162.
For the normal operation of the switches 160, the LEDs 170 cannot be placed right below the key tops 140. Since visible light emitted from the LEDs 170 passes through the elastic pad 120 and illuminates the key tops 140 at an oblique angle, each key top 140 itself is indirectly and unevenly illuminated. Accordingly, the center of each key top 140 is relatively dark, while the perimeter is bright. A larger number of LEDs may be mounted to more uniformly and brightly illuminate the key tops 140, which however increases power consumption and cost of manufacture.
Since the visible light emitted from the LEDs 170 leaks out to the upper surface 122 of the elastic pad, it may deteriorate the appearance of the keypad assembly 100. Particularly, if the keypad assembly is mounted within a thin and bright-colored housing, the degree of light leakage will be increased. Although various mechanical solutions, such as a black printed film, have been suggested, none of them is completely satisfactory to solve the light leakage problem.